AND CORROSION PROTECTION OF METALS
Russian Journal of Applied Chemistry, 2012, Vol. 85, No. 1, pp. 52−56.
Pleiades Publishing, Ltd., 2012.
Original Russian Text © G.I. Medvedev, N.A. Makrushin, 2012, published in Zhurnal Prikladnoi Khimii, 2012, Vol. 85, No. 1, pp. 55−59.
Electrodeposition of Tin–Cobalt Alloy from a Sulfate
Electrolyte with Organic Additives
G. I. Medvedev and N. A. Makrushin
Novomoskovsk Institute, Mendeleev Russian University of Chemical Engineering, Novomoskovsk, Tula oblast, Russia
Received July 15, 2011
Abstract—Electrodeposition of a tin–cobalt alloy from a sulfate electrolyte with organic additives was studied.
A tin–cobalt galvanic alloy with a cobalt content of
up to 1 wt % is successfully used in coatings for various
solderable assembling articles. These coatings remain
solderable in storage for no less than 1.5 years under
warehouse conditions and show no needle-formation
or allotropic transformations at low temperatures, typi-
cally observed for pure tin. Chloride-ﬂ uoride, sulfate-
ﬂ uoride, and sulfate electrolytes with organic additives
was developed for electrodeposition of the Sn–Co alloy
A rather promising research area related to electro-
deposition of tin alloys consists in examination of elec-
trodeposition conditions of bright coatings in the course
of the electrolysis itself. Bright coatings are less porous,
and their hardness and corrosion resistance are higher.
In this case, no reﬂ owing of coatings is required before
soldering. Baths for bright plated coatings are, as a rule,
operated at higher current densities, which intensiﬁ es
Previously, a sulfate-ﬂ uoride electrolyte for
deposition of bright Sn–Co coatings has been developed
. In this electrolyte, the role of a brightening additive
is played by a rather complex mixture of alcoholic
solutions of ortho-anisidine and cinnamic aldehyde and
products of their interaction (N-3 additive), combined
with a wetting agent, nonionogenic surfactant, and
Studies of the electrodeposition of the Sn–Co alloy
from a sulfate electrolyte with organic additives (DS-
10 synthanol and formalin) have shown  that the
bright-forming effect is exhibited by organic substances
with an ionization potential in the range 8.7–10.5 eV.
Taking this circumstance into account, we studied the
electrodeposition of the Sn–Co alloy from a sulfate
electrolyte containing DS-10 synthanol, formalin, and
coumarin, whose ionization potential is 8.97 eV. The
study was performed in the electrolyte of composition
(g l–1): SnSO
DS-10 synthanol 1–3, coumarin 1–5, formalin (37%
solution) 2–8 ml l–1 at a temperature of 18–25°C.
Pure tin of 01 brand served as anodes. The alloy was
deposited onto copper samples. The alloy coating
thickness was 9–12 μm. The electrolyte was agitated
with a mechanical rabble.
Polarization curves were measured on a P-5827
potentiostat. The alloy was analyzed by the procedure
described in , and the microhardness of the coatings,
with the MPT-3 instrument . The leveling power of
the electrolyte was determined by the method described
in . The solderability of the coatings was examined
by the method of solder portion spreading, with the
solder spreading coefﬁ cient determined .
The effect of the concentration of organic substances
on the outward appearance of the coatings was
examined in an electrolyte containing (g l
30, and H
90. Experimental results
demonstrated the bright coatings are obtained only in
the case of a simultaneous presence in the electrolyte
of synthanol (1–3 g l
), formalin (37% solution,
5–6 ml l
), and coumarin (1–2 g l
). Deviations from
these concentration limits result in that semibright,
matte, and rough surfaces are obtained, depending on